White-Throated Sparrow Feathers

Traditionally juvenile birds grow all their feathers in the nest over a short time period while adult birds incrementally molt their feathers over a longer time period. Therefore, there may be different energetic demands which mediate differences in composition of feathers between adult and juvenile birds. White-throated Sparrows are a polymorphic species, so there may also be differences between sex and morph. Here we perform a t-test, two-way ANOVA, and ANCOVA to investigate differences between basic and juvenile White-throated Sparrow P4 feathers, as well as other morphometric features. More information on White-throated Sparrows can be found here.

Figure 1. Open wing primaries of a basic plumage (left) and juvenile plumage (right) White-throated SparrowFigure 1. Open wing primaries of a basic plumage (left) and juvenile plumage (right) White-throated Sparrow

Figure 1. Open wing primaries of a basic plumage (left) and juvenile plumage (right) White-throated Sparrow

Welch Two Sample T-test

First we will create a gtsummary table which performs a Welch two sample t-test comparing mean P4 mass (g), P4 length (mm), wing chord length (mm), and tail length (mm) for birds with juvenile and basic P4 feathers. Note that the categories for juvenile and basic only refer to P4 and are not a meaningful category for wing chord and tail length, and are only included for the purpose of this assignment.

Table 1. Summary characteristics and counts of White-throated Sparrow P4 feathers sampled
Basic Juvenile
Sex
    F 8 (42%) 46 (39%)
    M 11 (58%) 71 (61%)
Morph
    TS 12 (63%) 54 (46%)
    WS 7 (37%) 63 (54%)
Mass (mg) 9.5 (1.0) 9.1 (0.9)
Length (mm) 62.2 (2.6) 61.8 (2.3)
Table 2. Mean (sd) values of morphological characteristics for White-throated Sparrows with either juvenile or basic P4 feathers. A Welch two sample t-test was used to generate the P-value for each characteristic
Basic Juvenile P-value
P4 Mass (mg) 9.5 (1.0) 9.1 (0.9) 0.10
P4 Length (mm) 62.2 (2.6) 61.8 (2.3) 0.52
Wing Chord (mm) 72.8 (3.3) 72.0 (2.6) 0.33
Tail Length (mm) 73.2 (2.6) 72.9 (2.7) 0.66
Figure 2. Comparison of mass (left) and length (right) for both juvenile and basic P4 feathersFigure 2. Comparison of mass (left) and length (right) for both juvenile and basic P4 feathers

Figure 2. Comparison of mass (left) and length (right) for both juvenile and basic P4 feathers

ANOVA

For the ANOVA we will group by age categories for the purpose of this assignment. These age categories may not represent an ecologically significant category as HY birds become classified as SY birds after January 1.

Table 3. Mean (sd) values for morphological characteristics of White-throated Sparrows of different ages. An ANOVA was used to generate the P-value for each characteristic
AHY ASY HY SY P-value
P4 Mass (mg) 9.4 (1.1) 9.9 (0.7) 9.2 (0.9) 9.1 (0.9) 0.17
P4 Length (mm) 61.6 (2.6) 63.6 (1.5) 62.1 (2.2) 61.4 (2.4) 0.10
Wing Chord (mm) 72.6 (3.1) 74.2 (2.4) 72.4 (2.4) 71.5 (2.8) 0.052
Tail Length (mm) 72.8 (1.9) 74.7 (2.3) 73.1 (2.8) 72.6 (2.7) 0.29
Figure 3. Comparison of P4 mass for different age categories of White-throated Sparrow

Figure 3. Comparison of P4 mass for different age categories of White-throated Sparrow

ANCOVA

For the Ancova we will be investigating the response variable of P4 mass based on predictors of P4 feather length and P4 feather generation. This should remove the effect length has on mass so that we may better understand how feather generation affects the mass of a White-throated Sparrow Feather.

Table 4. Comparison of juvenile and basic P4 mass (mg) adjusted for P4 length (mm). An ANCOVA was used to adjust means and generate summary statistics
Basic(N=19) Juvenile(N=19) Adjusted Difference 95% CI1 p-value
P4 Mass (mg) 9.5 (1.0) 9.1 (0.9) 0.29 0.05, 0.53 0.019
Wing Chord (mm) 72.8 (3.3) 72.0 (2.6) 0.39 -0.26, 1.0 0.2
1 CI = Confidence Interval
Figure 4. Regression of feather mass and length for juvenile and basic P4 feathers

Figure 4. Regression of feather mass and length for juvenile and basic P4 feathers